Growth stage-dependent responses of arbuscular mycorrhizal fungi to nitrogen fertilization in maize-soybean intercropping

Arbuscular mycorrhizal fungi (AMF) are key to facilitating crop nitrogen and phosphorus uptake and soil nutrient cycling. Our previous research has shown that intercropping can enhance AMF diversity. However, the changes of AMF diversity and community structure in rhizospheric soil of intercropped maize at various growth stages under nitrogen fertilizer application remain to be further investigated. Therefore high-throughput sequencing methods were used to analyze the AMF community structure and soil chemical properties of intercropped maize at different growth stages under two nitrogen fertilizer application rates in a multi-year fixed-site field experiment. The results showed that the highest colonization rate of intercropped maize was observed at filling stage and was significantly higher than that of monoculture maize across all growth stages ( p < 0.05). With the growth of maize, the diversity of AMF and relative abundance of Glomus increased in the rhizosphere soil of maize showed upward trends and its abundance in intercropped maize increased by 32.45% compared with that of monoculture maize. The Shannon index in NF treatment was significantly lower than that in CN treatment ( p < 0.05) at mature stage. The results of network analysis showed that the complexity of the AMF network structure was the highest at filling stage. Moreover, the network complexity of the intercropping in NF treatment become even higher. Mantel analysis indicated that at mature stage, Paraglomus and Glomus were extremely significantly correlated with soil pH, SOC and AN. SEM analysis further indicated that nitrogen application was significantly negatively correlated with soil chemical properties, while intercropping directly increased the abundance of AMF structure through interspecific competition. This study suggested that crop diversity under different nitrogen fertilizer application rates mediated AMF-dynamic changes at different growth stages through the changes of soil nutrients due to interspecific interaction.